LXR linux/kernel/kcsan/encoding.h

   1/* SPDX-License-Identifier: GPL-2.0 */
   2
   3#ifndef _KERNEL_KCSAN_ENCODING_H
   4#define _KERNEL_KCSAN_ENCODING_H
   5
   6#include <linux/bits.h>
   7#include <linux/log2.h>
   8#include <linux/mm.h>
   9
  10#include "kcsan.h"
  11
  12#define SLOT_RANGE PAGE_SIZE
  13
  14#define INVALID_WATCHPOINT  0
  15#define CONSUMED_WATCHPOINT 1
  16
  17/*
  18 * The maximum useful size of accesses for which we set up watchpoints is the
  19 * max range of slots we check on an access.
  20 */
  21#define MAX_ENCODABLE_SIZE (SLOT_RANGE * (1 + KCSAN_CHECK_ADJACENT))
  22
  23/*
  24 * Number of bits we use to store size info.
  25 */
  26#define WATCHPOINT_SIZE_BITS bits_per(MAX_ENCODABLE_SIZE)
  27/*
  28 * This encoding for addresses discards the upper (1 for is-write + SIZE_BITS);
  29 * however, most 64-bit architectures do not use the full 64-bit address space.
  30 * Also, in order for a false positive to be observable 2 things need to happen:
  31 *
  32 *      1. different addresses but with the same encoded address race;
  33 *      2. and both map onto the same watchpoint slots;
  34 *
  35 * Both these are assumed to be very unlikely. However, in case it still
  36 * happens, the report logic will filter out the false positive (see report.c).
  37 */
  38#define WATCHPOINT_ADDR_BITS (BITS_PER_LONG-1 - WATCHPOINT_SIZE_BITS)
  39
  40/* Bitmasks for the encoded watchpoint access information. */
  41#define WATCHPOINT_WRITE_MASK   BIT(BITS_PER_LONG-1)
  42#define WATCHPOINT_SIZE_MASK    GENMASK(BITS_PER_LONG-2, WATCHPOINT_ADDR_BITS)
  43#define WATCHPOINT_ADDR_MASK    GENMASK(WATCHPOINT_ADDR_BITS-1, 0)
  44static_assert(WATCHPOINT_ADDR_MASK == (1UL << WATCHPOINT_ADDR_BITS) - 1);
  45static_assert((WATCHPOINT_WRITE_MASK ^ WATCHPOINT_SIZE_MASK ^ WATCHPOINT_ADDR_MASK) == ~0UL);
  46
  47static inline bool check_encodable(unsigned long addr, size_t size)
  48{
  49        /*
  50         * While we can encode addrs<PAGE_SIZE, avoid crashing with a NULL
  51         * pointer deref inside KCSAN.
  52         */
  53        return addr >= PAGE_SIZE && size <= MAX_ENCODABLE_SIZE;
  54}
  55
  56static inline long
  57encode_watchpoint(unsigned long addr, size_t size, bool is_write)
  58{
  59        return (long)((is_write ? WATCHPOINT_WRITE_MASK : 0) |
  60                      (size << WATCHPOINT_ADDR_BITS) |
  61                      (addr & WATCHPOINT_ADDR_MASK));
  62}
  63
  64static __always_inline bool decode_watchpoint(long watchpoint,
  65                                              unsigned long *addr_masked,
  66                                              size_t *size,
  67                                              bool *is_write)
  68{
  69        if (watchpoint == INVALID_WATCHPOINT ||
  70            watchpoint == CONSUMED_WATCHPOINT)
  71                return false;
  72
  73        *addr_masked =    (unsigned long)watchpoint & WATCHPOINT_ADDR_MASK;
  74        *size        =   ((unsigned long)watchpoint & WATCHPOINT_SIZE_MASK) >> WATCHPOINT_ADDR_BITS;
  75        *is_write    = !!((unsigned long)watchpoint & WATCHPOINT_WRITE_MASK);
  76
  77        return true;
  78}
  79
  80/*
  81 * Return watchpoint slot for an address.
  82 */
  83static __always_inline int watchpoint_slot(unsigned long addr)
  84{
  85        return (addr / PAGE_SIZE) % CONFIG_KCSAN_NUM_WATCHPOINTS;
  86}
  87
  88static __always_inline bool matching_access(unsigned long addr1, size_t size1,
  89                                            unsigned long addr2, size_t size2)
  90{
  91        unsigned long end_range1 = addr1 + size1 - 1;
  92        unsigned long end_range2 = addr2 + size2 - 1;
  93
  94        return addr1 <= end_range2 && addr2 <= end_range1;
  95}
  96
  97#endif /* _KERNEL_KCSAN_ENCODING_H */
  98